Paper stiffened with bark extractives and method of making the same



United States Patent 3,359.261 PAPER STIFFENED WITH BARK EXTRACTIVES ANDMETHOD 0F MAKING THE SAME James R. Roberts, Paiatine, 111., and ArthurS. Gregory,

Tacoma, and Richard M. Morris, Longview, Wash., assignors toWeyerhaeuser Company, Tacoma, Wash, a corporation of Washington NoDrawing. Continuation of application Ser. No. 236,142, Nov. 7, 1962.This application May 12, 1966, Ser. No. 550,880

11 Claims. (Cl. 162-117) This application is a continuation of Ser. No.236,142, filed Nov. 7, 1962 and now abandoned.

This invention relates to the paper making art, and more particularly toa paper made from the common species of cellulosic materials andcharacterized by a high degree of stiffness and structural strength, andto the method of its manufacture.

Conventional methods of providing stiffened papers heretofore haveinvolved the use of special cellulosic pulps which impart inherentstiffness to the paper, or the coating or impregnation of conventionalpaper stocks with special stiffening agents. However, these methods areeconomically disadvantageous in the following respects: The specialcellulosic pulps are too costly for the limited degree of improvementwhich they impart to the paper. The special stiffening agents either aretoo costly or they present such problems as hazardous and difiicultapplication, unfeasible waste recovery, poor glueability, and fragilityof the treated paper.

For example, sodium silicate has been employed as a low cost stiffeningagent, but the treated paper is too brittle for such uses as corrugatedmedium. Additionally, the treated paper exhibits poor glueability andhence is not practical for such uses as liner for corrugated boxmaterial. Sulphur has been used as a stiffening agent, and although itsunit cost is reasonably low the large amount require-d to be added topaper to achieve a reasonable degree of stiffness reflects an excessivecost to the finished product. Moreover, it is extremely hazardous anddifficult to apply, its waste recovery is not economically feasable, andthe treated paper exhibits poor glueability.

Synthetic resins of various types also have been employed as specialstiffening agents, and while they impart to the paper increasedstiffness, they tend to decrease flexibility and ease of corrugating andtheir high cost renders the product economically undesirable for generaluse.

Accordin ly, it is the principal object of the present invention toprovide a stiffened paper from common species of cellulosic fibroussources by a method which utilizes low cost raw material, which may beperformed in conjunction with conventional types of paper makingmachinery at conventional production speeds, and which is capable ofincreasing the stiffness of paper without adversely affecting itsstrength or other desirable properties.

The foregoing and other objects and advantages of this invention willappear from the following detailed description.

In its broad concept, the present invention involves the impregnation ofthe cellulosic fiber of paper after formation of the sheet, with atreating solution consisting essentially of the alkaline solubleconstituents of the barks of trees. Preferably, the solution is appliedto one or both sides of a preformed sheet of paper stock, after thelatter has been drained or dried, and the application is made in suchmanner as to effect pickup of from 0.5 to 15% or more solution solids byweight, dry sheet basis.

The method of this invention is applicable to any of the conventionalpaper making pulps derived from Wood,

3,35%,261 Patented 0st. 31, 1967 straw, bagasse, and likelignocellulosic materials. Further, it is applicable to pulps made bychemical, semichemical or mechanical methods.

The alkaline soluble constituents may be derived from the barks ofconiferous or deciduous trees, the barks of the Douglas fir and Westernhemlock being preferred for their availability.

In general, extraction of the bark may be effected with any alkalinesolution and under all conditions of treatment which will achieveeconomically feasible extraction in good yield. In the preferredprocedure, the alkaline bark extract is prepared by feeding bark inparticulate form to a two stage countercurrent extraction processwherein it is subjected to the action of an aqueous alkaline solutionfor a time predetermined to dissolve the alkali soluble content of thebark.

The alkaline solution is prepared from a basic acting compound of analkali metal or ammonia, preferably caustic soda, sodium carbonate,caustic potash, or ammonium hydroxide, in an amount ranging from 5 to25% by weight, preferably 10 to 16% in the case of caustic soda, drybar-k basis. The ratio of bark to aqueous media also is controlled toproduce an alkaline extract having an organic solids concentration offrom 5 to 25%.

The extraction is conducted at a temperature between ambient temperatureand the boiling point of the extractor contents at atmospheric pressure,or at a higher temperature if super-atmospheric pressures are employed.Reaction time may vary from 10 to 180 minutes, preferably from 30 tominutes.

Upon completion of the reaction, the aqueous alkaline slurry is passedthrough a separator where the large insoluble bark solids are separatedfrom the liquid. The insoluble bark fines carried with the liquid thenare removed, preferably by centrifuging.

The foregoing alkaline extract contains a complex mixture of organicchemicals, which either are present as such in the original bark, or arederived therefrom by hydrolysis or other chemical reaction during thealkaline extraction, including the following classes of material.

Waxy components:

Salts of fatty acids Salts of hydroxy fatty acids Salts of phenolicfatty acid esters Neutral esters of fatty acids Long chain alcoholsSterols Non-waxy components:

Salts of monomeric and polymeric phenolic substances Salts of monomericand polymeric phenolic acid substances The complex mixture comprisingthe alkaline extract may be employed per se for the purpose of thepresent invention. Alternatively, the mixture may be treated for removalof its wax fraction since it has been found that the wax-free fractionprovides higher concora values than the untreated mixture. In eithercase the solution may be dried and the dried solids. redispersed inwater to provide a treating solution.

The solids content of the treating solution may range from 5 to 25%,preferably about 15%, the upper limit being determined primarily by theviscosity of the solution at the application temperature. In general,the application temperature may vary between ambient temperature and theboiling point of the solution, preferably between F. and the boilingpoint which may be slightly above the boiling point of water. Highertemperatures with pressure are also possible. It is desirable that thesolids content and temperature of the solution e in be as high aspracticable, while providing a viscosity sufficiently low for eifectiveapplication.

It is also desirable that the paper sheet be formed from an aqueousslurry of fibers in such manner as to provide the characteristics offreeness, Cobb and porosity, consistent with its ultimate strengthrequirements, that give to the paper a high ability to pick up theaqueous solution. In this latter regard, solution solids pickup into thepaper may range from 0.5 to more than 15% by Weight, dry fiber basis.

Since tests indicate that the solution solids penetrate into thecellulosic fibers, as well as collecting between the fibers, it has beenfound that a maximum increase in stiffness is achieved by applying thetreating solution after the sheet has drained and partially dried.Accordingly, it has been found desirable to add the treating agent inthe vicinity of the size press. Application of the solution may beeffected by dipping the paper in the solution, or by depositing thesolution upon one or both surfaces of the paper by means of spraynozzles or rolls.

Conveniently, the solution is applied intermediate the ends of the drierroll assembly, at a point where a sufiicient number of drying rollsstill remain to achieve proper reduction in moisture content of thepaper. Thus, for example, in a conventional drying assembly of about 50rolls, the solution may be applied in the vicinity of the 40th roll.

It will be understood that the feed rate of the solution to the paper,to achieve a desired degree of pickup, varies with the web speed,characteristics of the paper sheet being formed, solids content of thesolution, and other factors.

The treated paper may be employed per se for various commercialapplications, such as liner for the production of corrugated box board.It may also be used as the corrugated medium, in which case the treatedpaper is passed through conventional corrugating apparatus. In thislatter regard it has been found desirable to precondition the sheet witha greater amount of steam than ordinarily employed, to assure uniformityof moisture content throughout the sheet and to provide a slightlyhigher temperature in the sheet for most effective results at thefluting rolls.

The corrugated paper then is passed through conventional glue applyingapparatus where glue is applied to the crests only of the corrugatedmedium. Face sheets then are applied to the opposite sides of thecorrugated medium and the assembly pressed and cut to appropriatelengths.

The following examples are illustrative of the present invention:

EXAMPLE I Unbleached 38 pound and 42 pound kraft paper samples weretreated at the size press with varying concentrations of an aqueoussolution containing alkali soluble constituents of bark at 150 F. and,after conditioning at 50% relative humidity and 72 F. for a minimum of24 hours, were tested for CLT improvement. The average results of thesetests are given in Table I.

TABLE I CLT, lbs. Extract Solids Solids, Pickup, Web Post Percent byPercent by Speed, Control Test weight weight .p.m.

MD CD MD CD 4 EXAMPLE 11 Twenty six pound neutral sulfite semi-chemicalpaper samples were treated on one side with bark extract aqueoussolution having varying percentages of alkali soluble solids, andcomparative concora tests with control sheets were conducted withoutpreconditioning. The test sheets then were corrugated on conventionalcorrugating apparatus at about 200 feet per minute and laminated with 42pound unbleached kraft paper, both sides. After conditioning at 50%relative humidity and 72 F. for 24 hours the corrugated paper productwas tested for flat crush and compression strength. The average resultsof these tests are set forth in Tables II and III.

TABLE II Solids Web Concora Test Extract Solids, Pickup, Speed, Percentby Weight Percent by f.p.m.

Weight Control Test 1. 5 800 68 82 4. 3 800 63 82 9. 3 800 64 68 2. 0 1,48 78 2. G 800 48 78 3. 25 800 48 96 (applied both sides) TABLE III FlatCrush, psi. Test Corrugator Speed, t.p.1n.

Control Test 1 Not corrugated1nsutfieient material.

EXAMPLE III Twenty six pound neutral sulfite semi-chemical paper samplesof varying porosity were treated with bark extract aqueous solutionhaving from 15 to 18% by weight alkali soluble solids at to F., todetermine the effect of porosity on the solids pickup and resultingconcora. In one test, paper having a porosity of 206 seconds per 100milliliters of air was treated at a web speed of 880 feet per minute.The solids pickup averaged 2.8% by weight and the concora 84 points. Ina second test, paper having a porosity of 145 seconds per 100milliliters of air was treated at a web speed of 900 feet per minute,resulting in an average solids pickup of 3.3% and a concora averaging 92points. In another test, paper having a porosity of 110 seconds per 100milliliters of air was treated at a web speed of 960 feet per minute,resulting in an average solids pickup of 3.5% and a concora averaging 95points.

EXAMPLE IV Twenty six pounds neutral sulfite semi-chemical paper sampleswere treated with separate bark extract aqueous solutions both havingabout 12% by weight alkali soluble solids. However, one of the solutionswas centrifuged to remove the insoluble bark fines. The paper treatedwith the solution containing the bark fines picked up an average of4.04% by weight solids and, after conditioning at 50% relative humidityand 72 F. for 24 hours, had an average concora of 94 points as comparedwith 74 points for the control. The same paper treated with the solutionin which the bark fines were removed, picked up an average of 5.14% byWeight solids and the conditioned sheet had an average concora of 116points.

EXAMPLE v EXAMPLE VI To illustrate the eifect of applying the liquorsolution at various points between the wet and dry ends of the paper, 26pound neutral sulfite semi-chemical paper was treated with bark extractaqueous solution separately at the No. 5, No. 21 and No. 41 drier rolls,in a 51 drier roll assembly, by spraying the solution (11.6% alkalisoluble solids) at a temperature of about 150 to 160 F. The results ofthis test are shown in the following table, the concora values beingdetermined after conditioning at 50% relative humidity and 72 F. for 24hours:

TABLE IV Treatment Location Solids Pick-Up, Concora Percent by weightControl 66. 68 No. 5 RolL- 4.03 70 No. 21 Roll. 4. 62 81 No. 41 R011 2.93 88 In the above examples, the flat crush and box compression testswere made according to ASTM Standards D1225-54 and D-642-47respectively. The CLT test is a well known test in the industry andconsists of cutting a strip 6 inches long and /2 inch wide, clamping thesame on edge between platens with A inch exposed and then compressingbetween the platens of an H & D tester and recording the pressure inpounds to crush the exposed edge. Likewise the concora test is wellrecognized in the industry, consisting of providing flutes in a striporiginally 6 inches long and /2 inch wide, placing the corrugated stripon a strip of pressure sensitive adhesive tape and placing it betweenthe platens of an H & D tester as mentioned above. The H & D tester andattachments are sold by Testing Machines, Incorporated, New York city,and is a standard piece of testing equipment throughout the industry.

From the foregoing it will be apparent that by the present inventionpapers produced from the common species of cellulose fiber material maybe stiffened to a substantial degree at minimum cost, rendering thetreated paper suitable for many commercial uses including the productionof corrugated medium and liners. Furthermore, the treated paper of thisinvention may be run on corrugating machines at speeds up to 620 feetper minute which is the same as for untreated papers and greater thanthe speeds capable of being attained with other treated papers.Production costs are further minimized by enabling the process to beintegrated into conventional paper making processes with minimumadditional equipment and with no reduction in plant production speed.Production data also shows that in contrast to almost all othercontainer boards containing additives, the waste treated paper of thisinvention can be easily repulped and reprocessed for further paperproduction.

It will be apparent to those skilled in the art that various changes maybe made in the procedural steps, proportions of ingredients and otherprocess conditions disclosed hereinafter, without departing from thespirit of this invention and the scope of the appended claims.

Having now described our invention, we claim:

1. The method of making stiifened paper, comprising forming the paperfrom an aqueous slurry of fibers, removing a substantial proportion ofthe water from the formed paper, applying to at least one surface of thepaper an aqueous solution containing alkali soluble constituents of treebark substantially free of alkali insoluble bark solids, and thereafterdrying the paper.

2. The method of claim 1 in which said paper is corrugating medium, andincluding the additional step of fluting said paper.

3. The method of claim 1 in which said aqueous solution containingalkali soluble constituents of tree bark is substantially wax free.

4. The method of claim 3 in which said paper is corrugating medium, andincluding the additional step of fluting said paper.

5. The method of claim 1 in which said aqueous solution containingalkali soluble constituents of tree bark has a solids content rangingfrom 5 to 25% by weight, and in which 0.5 to 15% by weight, dry fiberbasis, of said solids is added to said paper.

6. The method of claim 5 in which said paper is corrugating medium, andincluding the additional step of fluting said paper.

7. The method of claim 5 in which said aqueous solution containingalkali soluble constituents of tree bark is substantially wax free.

8. The method of claim 7 in which said paper is corrugating medium andincluding the additional step of fluting said paper.

9. The method of claim 1 in which said aqueous solution is at atemperature of from ambient to the boiling point of the solution.

10. The method of claim 9 in which said paper is corrugating medium andincluding the additional step of fluting said paper.

11. The product formed by the process of claim 1.

References Cited UNITED STATES PATENTS 1,280,400 10/1918 Clapp 162-111,828,029 10/1931 Marx 16293 X 2,698,233 12/1954 Lewis 162-93 X2,781,336 2/1957 Zenczak 106163 2,823,223 2/ 1958 Steinberg 16293 X2,840,138 6/ 1958 Johnston 117-158 FOREIGN PATENTS 587,237 11/1959Canada.

DONALL H. SYLVESTER, Primary Examiner. HOWARD R. CAINE, AssistantExaminer.

1. THE METHOD OF MAKING STIFFENED PAPER, COMPRISING FORMING THE PAPERFROM AN AQUEOUS SLURRY OF FIBERS, REMOVING A SUBSTANTIAL PROPORTION OFTHE WATER FROM THE FORMED PAPER, APPLYING TO AT LEAST ONE SURFACE OF THEPAPER AN AQUEOUS SOLUTION CONTAINING ALKALI SOLUBLE CONSTITUENTS OF TREEBARK SUBSTANTIALLY FREE OF ALKALI INSOLUBLE BARK SOLIDS, AND THEREAFTERDRYING THE PAPER.